Constraints on neutralino dark matter from LEP 2 and cosmology

A significant lower limit on the mass of the lightest neutralino χ can be obtained by combining the results from sparticle searches at LEP at centre-of-mass energies up to 172 GeV with cosmological considerations, if it is assumed that the χ is stable. Exclusion domains from slepton searches close m_χ ∼ 0 loopholes that were left open by previous lower-energy LEP searches for charginos and neutralinos, leading to the lower limit mχ ≳ 17 GeV. The constraints on supersymmetric parameter space are strengthened significantly if LEP constraints on supersymmetric Higgs bosons are taken into account, and further if the relic neutralino density is required to fall within the range favoured by astrophysics and cosmology. These bounds are considerably strengthened if universality at the GUT scale is assumed for soft supersymmetry-breaking scalar masses, including those of the Higgs bosons. In this case, the Higgs searches play a dramatic rôle, and we find that m_χ ≳ 40 GeV. Furthermore, we find that if tan β ≲ 1.7 for μ < 0, or tan β ≲ 1.4 for μ > 0, the cosmological relic density is too large for all values of m_χ.